Monoglycerides are widely used as emulsifiers as well as starch modifying agents. The affinity to starch renders them particularly useful in bakery products and other starch containing foods, for instance with respect to improving bread texture.
In bread, the monoglycerides prevent or reduce staling and thereby increase softness and shelf life. The theory is that staling to a great extent is caused by the retrogradation of the gelatinized starch, particularly of the amylose fraction of the starch. Amylose forms a helix and a monoglyceride molecule fits into this helix. A monoglyceride molecule entrapped in the amylose helix represents a water-insoluble complex which will not take part in the progressing retrogradation of amylose. Thereby the staling tendences are reduced.
In spaghetti, macaroni, noodles and similar products the monoglycerides ensure a firm, non-sticky consistency when the product is cooked.
Monoglycerides are of a polymorphic nature. In the solid state two substantially different crystal forms exist, an unstable .alpha. (alpha) crystal form and a stable and more compact .beta. (beta) crystal form. When suspended in a water phase and heated both crystal forms will hydrate and convert into an active state or form with affinity to starch and able to form a complex with amylose. Monoglyceride powder in .alpha.-crystal form gives the effects referred to above because the .alpha.-form at room temperature easily converts into an active amylose complexing state whereas ordinary monoglyceride powder in the .beta.-crystal form at room temperature is almost ineffective in this respect. It is, however, very difficult or even impossible to prepare a composition of monoglycerides in the .alpha.-crystal form retaining this crystal form for a reasonable period of time. This problem can be overcome in a rather satisfactory manner by ensuring that the stable .beta.-crystal form is converted into an active form during the baking process for the bread or heating process for the other types of products mentioned. As this conversion is ordinarily limited by the time available and the temperatures prevailing during baking processes or the processes used for preparing macaroni, noodles etcetera, it is necessary that the .beta.-crystals to convert are very small, i.e. that the monoglyceride product is very finely crystallized with a large surface exposed to the water phase. Furthermore, the monoglyceride must be extremely well distributed in the dough in order to achieve maximum effect thereof.
In present practice, monoglycerides for bread and other farinaceous products as mentioned are normally used in the form of a 25% dispersion made by admixing one part of monoglyceride into three parts of hot water. On cooling, the monoglyceride will form micro-crystals suspended in water. Just after the crystallization, a substantial portion of the polymorphic monoglyceride will be present in an .alpha.-crystal form. The .alpha.-crystals are thermodynamically unstable and on standing will be transformed into a stable .beta.-crystal form, still as very small particles.
If a freshly prepared dispersion is not agitated it will stiffen in course of the crystal transition period. To obtain a smooth paste, agitation is normally provided in the transition period, and the transition is accelerated by special means. Monoglyceride in this paste form is usually referred to as a "hydrate;" however, the water present is not water of crystallization in the normal sense. A hydrate prepared lege artis will be of full effect when added to a bread dough, and the effect of the monoglyceride can be observed as an improvement of the bread volume and the softness of the crumb, especially the softness after some days of ageing. The monoglyceride will increase volume and decrease crumb firmness. The reason is that the .beta.-crystals when present as described are intimately distributed in the dough and readily convert into an active form with affinity to starch during the baking process.
If, on the other hand, the monoglyceride in the stable .beta.-crystal form is added to the dough as an ordinary non-hydrated powder in the same dosage as the hydrate, calculated as the amount of dry monoglyceride, only a minor effect is observed. The reason probably is that under these circumstances, when the .beta.-crystal form is converted into an active form during the baking or other treating process the migration of the monoglyceride (having the active form) to the starch molecules is taking place locally only and is too slow to ensure the effect with respect to improving bread texture.
The dispersion or hydrate referred to above is normally prepared at central factories separate from the ultimate user thereof; the ultimate user will be the baker, the bread factory, the noddle, macaroni, spaghetti factory or the manufacturer of extruded snack-products. The reason is that the know-how involved in preparing the dispersions and the hydrates of monoglycerides is rather complicated if a first class product is to be obtained.
For obvious reasons it is desirable to supply a dry, free-flowing pulverulent product to the ultimate user. Firstly, thereby the cost of distributing comparatively large amounts of water (three times the amount of monoglyceride) would be saved and also the costs involved in packing a liquid paste rather than a powder; the latter could be packed simply in bags. Also, in many cases it is easier to admix a powder into the dough than a paste or liquid hydrate and also the pulverulent form would have the advantage that it could be admixed with the flour.